Process for the production of alkalineearth metals



y 7, 1959 E. WALASCHEWSKIYET AL 2,893,862

PROCESS FOR THE PRODUCTION OF ALKALINE-EARTH METALS Filed Sept. 19, 1956 2 Sheets-Sheet 1 INVENTORS Engelbert Walaschewski, Dieter Goerr-ig ATIDRNEKS July'7, 1959 E. WALASCHEWSKI ET AL 2,893,862

PROCESS FOR THE PRODUCTION- OF ALKALINE-EARTH METALS Filed Sept. 19, 1956 v 2 Sheets-Sheet 2 FIG. 6 F/G.8

INVENTOR.

ENGELBERT WALASCHEWSKI, D/ETER GOERP/G A T TORNEYS United States Patent PROCESS FOR THE PRODUCTION OF ALKALINE- EARTH METALS Engelbert Walaschewski, Koln-Bayenthal, and Dieter Goerrig, Lohmar, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany Application September 19, 1956, Serial No. 610,812 Claims priority, application Germany September 26, 1955 8 Claims. c1. 1s-4s7 This invention relates to a process for the production of alkaline-earth metals.

It is known, in the production of alkaline-earth metals, that it is possible to heat alkaline-earth hydrides, whereby hydrogen is split otf and the alkaline-earth metal is left in a more or less pure form, depending on the amount of impurities in the hydride. When the metal thus obtained is distilled, the major part of the impurities are left behind, but it is not possible to obtain a very pure metal in this way, since the distillate always contains nitrogen.

The present invention is concerned with a process for the production of pure alkaline-earth metals by heating alkaline-earth hydrides and distilling the alkaline-earth metal which is obtained, the said process consisting in preventing nitrogen from acting on the distilling metal. It has surprisingly been found that the nitrogen present in the hydride does not pass over with the distilling metal if the starting material subjected to the heating contains such a high content of aluminum that the nitrogen is fixed in the form of aluminium nitride.

In addition to the splitting of alkaline-earth hydrides into hydrogen and alkaline-earth metal, a number of other reactions take place during the thermal decomposition; thus, carbon, which may be present in elementary form or as carbonate, changes into alkaline-earth carbide, sulphur into sulphide and silicon compounds into silicides. These reactions all lead to compounds which are considerably less volatile than the alkaline-earth metals. nitrogen compounds of the alkaline-earth metals, however, decompose under the temperature and pressure conditions of the vaporisation of the metal and reform under the conditions under which the metal is condensed. For the production of pure alkaline-earth metals, it is consequently of decisive importance that the nitrogen in the material to be distilled can be fixed as aluminium nitride, since aluminium nitride has such a high decomposition temperature that the distillation of the alkaline-earth metals can take place without nitrogen being simultaneously split 01f.

The amount of aluminium or aluminium compounds, such as alumina, or aluminium alloys, such as calciumaluminium, which must be admixed with the initial material, which is to be distilled, depends of course on the amount of nitrogen contained in the initial hydride. If the initial hydride contains aluminium, the amount of aluminium to be added is reduced accordingly; in certain circumstances, the seperate addition of aluminium is unnecessary, if the crude hydride contains a suflicient amount of aluminium to ensure that the nitrogen present is fixed as nitride, for example 1.52% Al and 0.28% N.

0n heating the alkaline-earth hydrides to 1000ll50 C. at normal pressure, about 50% of the hydrogen present is split off, while the major part of the residual hydrogen is split off with further heating at 1l50-l350 C. with formation of more or less highly impure liquid alkaline-earth metals, which start to vaporise at temperatures above 1400 C. and yield a pure metal condensate when the distillation is completed at 1600 C. The proc- 2,893,862 Patented July 7, 1959 ice I ess is advantageously carried out at reduced pressure, so that the splitting and distillation is carried out at temperatures below 1000 C. and pressures of a few hundred mm. Hg to less than 10* mm. Hg.

The pure alkaline-earth metal thus produced and distilled in the presence of aluminium still always contains nitrogen, even if in very smallquantities. The occurrence of these amounts of nitrogen is avoided accordingto the invention if the metal vapour. is passed through highly efiicient dust separators, for it was established that nitrogenous fractions in powder form are extracted by the distillation from the solid phasev and are includedin the metal in the condensation. There are employed as dust separators combinations of filterssuch as are used in moderate. coarse vacuum and high vacuum work.

Very small amounts of nitrogen are still present in the alkaline-earth metal which is condensed after extremely careful filtration of the metalvapour. According to the invention, an alkaline-earth metal is. obtained which is practically completely free from nitrogen if the decom-. position of the hydride and the distillation of the metal is carried out in apparatus of which the outer walls are cold; it has in fact been found that the said'small amounts of nitrogen result from diffusion of nitrogen through hot apparatus walls. According to v the invention, for example apparatus having double walls are used, ins'ulatingmaterial being provided between the said walls in order that the rise intemperature of the outside walls is kept within narrow limits or is completely prevented.

The process according to thepresent invention is excellently suitable for the production of alkaline-earth metals from thetechnical hydrides which can be obtained The i according to conventional methods,

One embodiment of an apparatus which can be used for the preparation of ultra-pure alkaline-earth metals according togthe invention is illustrated in the accompanying drawings.

Figure -l is a longitudinal sectional view of the apparatus. r

A reaction vessell is heat-insulated by means of an insulation 2 inside which is arranged a chrome-nickel vessel 3 adaptedto-be-heated to the reaction temperature by the electrical heating system 4. Arranged at thebase of the reaction vessel is a supply pipe 5 for argon or another inert gas, while a connection 6 for a vacuum pump is provided at the top of the reaction vessel 1. Projecting from above into the reaction vessel 1 is a cooling arrangement 7 with supply and discharge devices 8 and 9 for a coolant, such as cooling water. The distilled metal 10 is precipitated atthis cooling arrangement; The starting material 11 is located at the bottom of the chromenickel vessel 3. The metal distilled out of the said material 11 passes in gaseous form through the dust filter 12. A circulation pump 13 is provided between the vacuum connection 6 and the argon supply pipe 5.

Figure 2v is a plan view and Figures 3 and 4 are crosssections of filter arrangements for the dust precipitation, the said filters consisting essentially of inclined metal plates 14 and a metal screen 15, it being possible for the said screen 15 to be arranged below the inclined metal plates 14, as shown in Figure 3, or above said plates, as shown in Figure 4.

Figure 5 is a plan view and Figure 6 is a cross-section of another constructional form of a dust separator, this consrstmg essentially of perforated plates 16 with perforations offset from one another and a metal screen 15.

Another constructional form of a dust separator is shown in Figures 7 and 8, Figure 7 being a plan view and Figure 8 a cross-section. It consists essentially of two or more concentric annular discs arranged in spaced superposed relation, the diameters thereof decreasing in the upward direction; the discs 17 are covered by a plate screen 15 is disposed underneath the said arrangement.

The invention is further illustrated by the following example without being restricted thereto. 7

Example 1 i 12.5 kg. of technical calcium hydride of the composition (in percent by weight) with an efliective calcium hydride content of 72-73% is placed in the apparatus described above after having had added thereto 0.125 kg. of an aluminium-calcium alloy containing 50% of aluminium, and with the vacuum pump cooperating with a suction capacity of 50 cu. metres per hour, the mixture is heated by the electric heating system with a heating capacity of 8 kw. After 3 hours, a temperature of 900 C. and a pressure of 0.1 mm. Hg are reached. After switching on two mercury diifusion pumps, heating is continued for another hour with the full heating capacity and a pressure lower than 10-' mm. Hg until the temperature suddenly starts to rise to just 1000 C. The furnace is then cooled by pumping argon at a pressure of 6 atm. gauge by means of a circulation compressor through the furnace. 8.1 kg. of calcium metal with a purity of 99.98% are obtained at the cooling arrangement.

Total analysis yields:

Analogous results are obtained when barium hydride with 52% BaH and a strontium hydride with 55% of SrH are processed in the same way.

We claim:

1. In the process for the production of an alkaline-earth metal having anatomic number between 20. and 56 by thermally splitting an alkaline-earth metal hydride into hydrogen and the respective alkaline/earth metal and distilling the alkaline-earth metal the step which comprises I '4 fixing the nitrogen present in the starting material in the form of aluminum nitride by performing the process in the presence of such an amount of aluminum which is at least chemically equivalent to the nitrogen amount present in the starting material. I

2. In the process for the production of an alkaline-earth metal havingan atomic number between 20 and 56 by thermally splitting an alkaline-earth metal hydride into hydrogen and the respective alkaline-earth metal and distilling the alkaline-earth metal the step which comprises fixing the nitrogen present in the starting material in the form of aluminum nitride by performing the process in the presence of such an amount of aluminum which is at least chemically equivalent to the nitrogen amount present in the starting material and filtering the earth-alkaline metal vapour so as to prevent the entraining of nitrogen containing dust into the distillate.

3. In the process for the production of an alkaline earth metal having an atomic number between 20 and 56 by thermally splitting an alkaline earth metal hydride containing such an alkaline earth metal into hydrogen and the respective alkaline earth metal,.and distilling the alkaline earth metal the step which comprises fixing the nitrogen present in the starting material in the form of aluminum nitride by performing the process in the presence of such an amount of an aluminum material selected from the group consisting of aluminum, an aluminum compound and an aluminum alloy, which is at least chemically equivalent to the nitrogen amount present in the starting material. 1

4. Process according to claim 3 in which said alkaline earth metal hydride is calcium hydride.

5. Process according to claim 3 in which said alkaline earth metal hydride is barium hydride.

6. Process according to claim 3 in which said alkaline earth metal hydride is strontium-hydride.

7. Process according to claim 3 which includes filtering the earth alkaline metal vapor so as to prevent the entraining of nitrogen containing dust into the distillate.

8. In the process for the production of an alkaline earth metal having an atomic number between 20 and 56 by thermally splitting an alkaline earth metal hydride containing such an alkaline earth metal into hydrogen and the respective alkaline earth metal and distilling the alkaline earth metal, the step which comprises fixing the nitrogen present in the starting material in the form of aluminum nitride by performing the process in the presence of such an amount of an aluminum material selected from the group consisting of aluminum, an aluminum compound and an aluminum alloy, which is at least chemically equivalent to the nitrogen amount present in the starting material and keeping the outer wall of the reaction space at a low temperature so as to prevent nitrogen from diifusing into the reaction space.

References Cited in the file of this patent UNITED STATES PATENTS 

2. IN THE PROCESS FOR THE PRODUCTION OF AN ALKALINE-EARTH METAL HAVING AN ATOMIC NEMBER BETWEEN 20 AND 56 BY THERMALLY SPLITTING AN ALKALINE-EARTH METAL HYDRIDE INTO HYDROGEN AND THE RESPECTIVE ALKALINE-EARTH METAL AND DISTILLING TH ALKALINE-EARTH METAL THE STEP WHICH COMPRISES FIXING THE NITROGEN PRESENT IN THE STARTING MATERIAL IN THE FORM OF ALUMINUM NITRODE BY PERFORMING THE PROCESS IN THE PRESENCE OF SUCH AN AMOUNT OF ALUMINUM WHICH IS AT LEAST CHEMICALLY EQUIVALENT TO THE NITROGEN AMOUNT PRESENT IN THE STARTING MATERIAL AND FILTERING THE EARTH-ALKALINE METAL VAPOUR SO AS TO PREVENT THE ENTRAINING OF NITROGEN CONTAINING DUST INTO THE DISTILLATE. 